Glass container coated with plastic containment film and method of making

ABSTRACT

A container having improved mechanical service strength and shatter resistance comprising a glass container body and a plastic containment coating film overlying the outside surface of the glass body. The mechanical properties of the film are such that, when subjected to tensile testing at room temperature and a film extension rate of 10 in./min., said film exhibits a tensile strength of at least about 300 lbs./sq. in., an elongation of at least about 80% and a modulus of elasticity in tension which is less than about 1,000 lbs./sq. in. substantially throughout the course of the extension of the film. The coating is substantially uniformly adhered to the glass body but with a peel strength of less than about 1.6 lbs./in. The desired peel strength may be provided by use of an adherency modifying primer coating which provides uniform adherence of the containment coating film to the glass body but limits that adherency to the desired peel strength.

United States Patent Brockway et al. Sept. 2, 1975 [54] GLASS CONTAINER COATED WITH 3,772.06! 1 H1973 McCoy ct a1. ll7/94 X PLASTIC CONTAINMENT LM AND 3.823.032 7/1974 Ukai 117/94 X METHOD OF MAKING Primary Eruminer-Ralph Husack Inventors: Clifford Bmckway; R'chard Attorney, Age/1!, in Firin-Koenig, Senniger, Powers Hunter, both of Columbus; Robert und Lem/m E. Sharpe, Worthington, all of Ohio [73] Assignee: Liberty Glass Company, Sapulpa, 57] ABSTRACT 1 Okla. A I I I contalner having improved mechanical servlce [22] F il edf May 25, 1973 strength and shatter resistance comprising a glass container body and a plastic containment coating film [2]] Appl' 364095 overlying the outside surface of the glass body. The mechanical properties of the film are such that, when 52] U.S. Cl .f. 428/35; 215/1 C; 2l5/D1G. 6; subjected to tensile testing at room temperature and a I 260/883; 427/407; 427/416; 428/429; film extension rate of lOin./min.; said film exhibits a 428/440; 428/441 tensile strength of at least about 300 lbs/sq. in.. an [51] Int. Cl. B65D 23/08; C03C 17/32 elongation of at least about 807: and a modulus of [58] Field of Search 117/124 E. 124 F, 72. 92, elasticity in tension which is less than about 1.000 117/94, 6, 161 UN; 215/1 C DIG. 6 lbs/sq. in. substantially throughout'the course of the extension of the filmfThe coating is substantially uni- [56] References Cited formly adhered to the glass body but with a peel I UNITED STATES PATENTS strength of less than about 1.6 lbs/in. The desired peel 2,923,646 2/1960 Jordan 117/161 UN l ll "W be f W use 9 afjherency 2 929.525 3/1960 Glover 25/1310 6 modifying primer coating wh1ch-prov1desun1form ad- 3IOO8V8SU 11/1961 ulrichm ll7/l6l UN x herence of the containment coating film to the glass 3131.077 4/1964 Barnby 117/124 E y but limits h h n y t0 h desired peel 3,328 482 6/1967 Northrup ct a1 l 17/124 F X Strength. 3503.918 3/1970 LeSota ct a1. 117/161 UN X 3.507.680 4/1970 Kiel 117 124 F x 19 C 9 Drawings GLASS CONTAINER COATED WITH PLASTIC CONTAINMENT FILM AND METHOD OF MAKING BACKGROUND OF T E [N vEN'noN This invention relates to the field of glass containers and moreparticularly to a container of improved mechanical service strength-andshatter resistance having a plastic containmenfl coating film whose adherence to the outside surface of the glass is limited so as to maximize the containment capability of the film.

In the container industry. substantial efforts have been devoted to developing methods for improving the impact and burst strength of glass containers without significantly adding to thecost of producing such containcrs. Improvement in impact and hurststrcngthcan providenot only important economic benefits. through reduced attrition, but can also make critical contributions to the personal safety of those who fill. handle and use glass containers.-. H

A substantial effort has been underway in the art to develop containment coatings which improve the resistance of a. glass beverage container to impact or burst failure. In recognition of the fact that prevention of such failure under all possible conditions of handling is an objective whose economicalattainment is very diffi cult, if not impossible, much effort has also been devoted to the development of means for mitigating the consequences of the failure of a glass container. Thus. important objectshave been to minimize both the de gree of. fragmentation, and the. extent of scatter of the fragments produced when a glass bottle fails.

Each of the properties of the impact resistance. burst strength. resistance to fragmentation and minimization of scatter ispartieularly important where a beverage bottle is used for packaging a carbonated beverage. Bottles for carbonated beverages are routinely exposed to incrnal pressures in the range of about50 psig. If and when such a bottle is broken; the resulting fragments. particularly if they are .very. small, can be propelled at high velocity by the carbon dioxide which is released. If these fragments strike a person, serious injuries may result. Occasionally a beverage bottle explodes due to the force of internal. pressure alone. Serious injuries have been caused by exploding beverage bottles.

As a means of improving the mechanical properties of beverage bottles in the above-noted respects. it has been proposed to provide such bottles with 21 containment": or protective coating. Compositions and processes are known. for example. which may be utilized to providea glass container with a rclatively thick coating of styrene foam. Styrene foam coatings are esthetically undesirable since they are white and opaque. thus preventing observation of the contents of the bottle. Glass containers are also known to have an outer lubricating film of polyethylene over an intermediate layer of a metal oxide such as a tin or titanium oxide for abrasion protective purposes. However, these in themselves do not provide satisfactory impact resistance and containment. i

As a result of the conditions encountered in the filling, handling and usage of a beverage bottle; a containment coating must meet a number or diverse criteria in addition to the mechanical properties noted above. Thus. in order to maintain its own integrity and effectiveness, the coating should be substantially resistant to abrasion. To avoid interference with visual observation of the bottles contents, the coating preferably pos- 2 sesses a high degree of clarity. To survive general usage and, in particular; to survive bottling plantprocessing, the coating should be resistant to both alkali and hot water. In order to minimize fire hazards in the-process of coating the bottle. the containment coating composition should not include significant proportions of flammable organic solvents, and desirably should be water based. Finally; the containment coating must hCinCX- pensiveto formulate and apply. failing which its use and application to beverage bottles are not feasible or practically economical. a j

An especially effective containment coating is that described in the copending and coassigned application of Brockway and Sharpe. Ser. No. 364.094. filed May 25,1973 which application is herein'explicitly incorporated by reference. In brief, Brockway and Sharpe describe a containment coating constituted by a plastic film which when subjected to tensile testing at a film extension rate of i0 in./min. exhibits a tensile strength of not "less than about 300 lbs./sq. 'in.',an elongationof notless than about 80% and a modulus ofelastieity in tension which is less than about 1.000 lbs/sq. in. throughout the course of the extension of the-film. A 2-4 mil-thick film having these mechanicalproperties has been demonstrated to afford superior containment as compared to that affordedby previously known containment coatings of similar thickness. Despite the remarkable containment provided by films having the aforesaid mechanical properties. however. pressurized beverage bottles coated with such films may stillufail with substantial scattering of fragments when subjected to sufficiently severe impact conditions. An important need continuesto exist, therefor, for further improvement in the mechanical service strength and scatter resistance obtainable by the use of plastic containment coating films.

SUMMARY OF THE INVENTION It is an object of the present invention, therefore. to attain further improvement in the mechanical service strength and shatter resistanee'afforded by the presence of a containment coatingon a'glass container. It is also an object of the present invention to provide such improvement without material sacrifice in the clarity or alkali resistance of the containment coating. ltisa fur ther object of the present invention to provide an improved method for the production of glass-containers having high mechanical service strength and shatter resistance. Other objects and features will be in part apparent and in part pointed out hereinafter.

Briefly, therefore, the present invention is directed to a container having improved mechanical service strength and shatter resistance comprising a glass container body and a plastic containment coating film overlying the outside surface of said body. The mechanical properties of the film are such that. when subjected to tensile testing at room temperature and a film extension rate of 10 in./min., the film exhibits a tensile strength of at leastabout 300 lbs./sq.in., an elongation of at least about 80% and a modulus of elasticity in ten sion which is less than about 1,000 lbs/sq. in. substantially throughout the course of the extension of the film. The film is substantially uniformly adhered to the outsidesurface of the glass body of the container but with a peel strength of less than about 1.6 lbs/in. The present invention is further directed to an improvement in a method for imparting improved mechanical strength toxacontainer having a glass body. In this 3 method a plastic containment coating film having the aforesaid mechanical properties is applied over the outside surface of the container. The improvement comprises applying an adherency modifying primer coating over the outside surface of said body prior to the application of the plastic containment coating film. The primer coating is effective to afford substantially uniform adherence of the plastic film to the glass body but with a peel strength of less than about L6 Ibs./in.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Although it has previously been recognized that the degree of adherence of an armor coating to a glass container may be an important factor affecting the overall strength of such a container. it has generally becneonsidered desirable to maximize such adherence in order to improve the mechanical properties of the container. For example. Smith and Wells US. Pat. No. 3.362.843 describes glass aerosol bottles having a relatively thick exterior coating of a vinyl resin adhered to theoutside of the bottle with a peel strength that is increased to as high as about 50 lbs/in. by use of a primer coating con taining methyl methocrylate. an epoxy resin and a. silane. More recently. however. it has been recognized that improved protection against shatter is achieved if there is only a slight adhesion between the glass and coating.

In accordance with the present invention. it has been 1 discovered that significantly improved containment properties are achieved by providing a plastic film containment coaating which is substantially uniformlyadhered to the outside surface of the glass body of a container. but with a controlled peel strength which is substantially less than the normal peel strength obtained when a plastic coating film is prepared by curing a precursor composition on the surface of the glass. The reasons for which a low degree of adherence isadvantageous are not fully understood. It is believed. however. that low adherence tends to reduce the. propensity of a fracture front in the glass body to propagate itself into the containment coating. perhaps by impeding or damping energy transmission from the glass to the plastic film.

As disclosed in the aforesaid application of Brockway 4 and Sharpe. highly advantageous containment is afforded by a plastic containment coating film whose properties are such that. when subjected to tensile testing at room temperature and a film extension rate of IO in./min.. the film exhibits a tensile strength of at least about 300 lbs/sq. in.. an elongation of at least about 8071 and a modulus of elasticity in tension which is less than about l.000 lbs/sq. in. substantially throughout the course of extension of the film. Such a film may be provided by dip coating a glass bottle or the like in an acrylic latex containing at least about 46.57: by weight resin solids constituted by a eopolymer containing about I27: by weight repeating units derived from acrylonitrile and about 857: by weight repeating units derived from ethyl acrylate. such as that sold under the trade designation Hycar 2679" by B. F. Goodrich Company. and curing the wet coating. I

For a containment coating film having the aforesaid mechanical properties. it has been found that containment is materially enhanced if the peel strength of the adherence of the containment film on the glass bottle is less than about 1.6 Ibs./in. as determined by slowly peeling a one half inch wide strip from the side of the 4 bottle by force applied normal to the side of the bottle. Preferably. the peel strength is even lower. i.e.. about I.() lb./in. or less, and a practical optimum peel strength for the adherence of such a containment film is considcred to be between about 0.60 and 0.70 Ib./in. From a containment standpoint alone. even lower peel strengths may be desirable but some minimum strength is necessary to insure substantially uniform adherence of the containment film to the glass body for purposes of appearance.

In accordance with the present invention. the desired limited degree of adherency may be provided by initially applying to the outside surface of the glass-body an adherency modifying primer coating which is effective to reduce the adherency of the containmentcoating to the desired extent. Among the adherency modifying primer coatings effective for this purpose are polyethylene. silicone resins and montan wax. A particularly useful source of polyethylene is the polyethylene emulsion sold under the trade designation SC- I 00 by New Jersey Specialty Chemicals lnc. Other satisfactory sources of adherency modifiers are the dimethyl silicone resin emulsions sold under the trade designations SM-2033 and SM2040" by General Electric.

An adherency modifying primer coating of polyethylene can conveniently be provided by spraying a polyethylene emulsion. such as SC-l00 over the outside surface of an uncoated bottle. or allternatively a bottle 'precoatcd with tetraisopropyl titanate. and drying the resultant wet primer coating. In a conventional glass bottle manufacturing operation. such a coating may be applied to the bottles emanating from the Iehr at a point where their temperature has dropped to approximately 250F. The residual heat retained by the bottles at this temperature facilitates the drying process. Aqueous emulsions of other adherency modifiers can be applied in a similar fashion. Alternatively. the adherency modifying primer coating may be applied in an organic solvent or directly as a molten liquid or powder coating.

Only a smsall amount of the adherency modifying primer coating is necessary to provide the desired degree of reduction in the peel strength for a subsequently applied plastic containment coating film. Thus. only about 0.0] mg./sq. in. of polyethylene will afford a significant reduction in the adherence of a conntainment film derived from an acrylic latex, and approximately 0.03 mg. of polyethyleneper sq. in. provides preferred adherency characteristics for a .film derived from a latex such as I-llycar 2679. The exact optimum amount of adherency modifying primer may vary somewhat dcpending on the identity of the primer and of the containment coating film but the proper amount can be readily determined by simple experimentation.

After the primer coating composition has been applied to the outside surface of the glass container and dried as necessary. the plastic containment coating film is applied over the outside surface of the primer coating. In a preferred embodiment of the invention. the container bearing the primer coating is dipped in a containment coating composition comprising an acrylic latex such as I-Iycar 2679. This coating composition may appropriately include thiekeners to impart a viscosity effective to provide the desired wet coating thickness. Cross-linkers may. also be included in the containment coating composition to promote high caustic resistance in the cured acrylic film.

D Curing of an acrylic latex is accomplished by any convenient method. for example. passage throughsa,

45(lF. in a forced-air oven. Certain of the bottles coated in this manner had been precoated with tetraisopropyl titanatc (a conventional glass coating agent others had been precoated with a polyethylene emullatex. such as Hyea r 2679. it is normally necessary that 3 sion sold under the trade designation SC-IOO, still othcurc conditions be carefully controlled in order to procrs had been precoatcd with a tetraisopropyl titanate vide sufficient curing for adequate caustic resistance followed by SC-lOl). and certain others had no precoat. but to avoid excessive curing which has been found to In some cases. the various precoats were applied by adversely affect containment properties. A unique adstandard production processes. while in others an SC- vantage of the method of the present invention is that ll) l()() coating was applied in the laboratory either on the presence of the adherency modifying primer coatbare glass or on a bottle which had received various ing allows a very thorough cure of the acrylic latex precoats in production facilities without any material adverse effect on containment. It The bottles which received the various combinations appears that excessive curing tends to promote too firm of prccoat and containment coating included both 10- a bond between film and glass but the presence of the l oz. and 16-02. beverage bottles. Containment tests primer coating interferes with such bonding and conwere conducted on both types of bottles. Preparatory trols adhercncy at the desired level. As a result. manuto these tests, the -02. bottles were filled with water facturing process control requirements are substaip leaving a l2-cc. head space and the lb-oz. bottles were tially less stringent and critical than they would othertilled with water leaving a ZZ-cc. head space All of the wise be. .and a consistently high degree of containment bottles were capped and pressurized to 57 psig with arcan be realized at relatively high production rates at gon. then dropped from a horizontal orientation ofthe low cost. bottle axis from a height of 4 feet onto a l/lo-inch The following examples illustrate the invention: thick vinyl asbestos tile supported on a l-foot square concrete block. Under these test conditions the glass EXAMPLE 1 35 bodies of all of the bottles failed. To determine the de- A containment coating composition was prepared gree of containment for each bottle. measurements containing 100 parts Hycar 2679 and 2 parts of a 171 were made of the percent bywcight of the bottle con solution of a polyacrylamide sold under the trade desigtained in the largest single cluster. and the weight distrination "Polyhall 295" by Stein Hall and Company. A bution of the fragments of the bottle about the point of number of beverage bottles were dip coated in this 30 impact. The results ofthcsc tests are set forth in Table composition and the wet coatings were air dried at 1. room temperature and then cured for 4 minutes at Table l.

Pre-Dip Spray Coating" Fragment Containment From Pressuri/cd Production Production -l Foot Drop Tests Applied Applied Distribution of Bottle As Fragments About The Point of Drop Impact. Percent Ex. None TPT TPT TPT Lab Dip Bottle Pccl Percent About Frag- Total Only Plus Plus Applied Applied Type Strength of The mcnts No. of

SC-l()() l.ab Ap- SC-ltltl Blend lb./in." Bottle Point of Inside Fracplied Only No 7 Com Frag- A ture SC-IUU Coating" tained in ments Radius Frag- Ap- Largest Residing of meats prosi- Single on 2%.- Ft. mate. Cluster Foot- From mils Square Center Impact of Block Impact A X none Standard clusters 24 82 I lt) oz. N.R. B X ll (Too high 20 34 9U to peel) C X 2.4 (Too high 2| 3U 9t) 2) to peel) I) X 2.4 (L78 )5 57 l()() 2 E X 2.2 0.68 )3 Sb lUU 5 F X l4 ltl o2. Coke (Too high I7 23 98 43 N.R. to peel G X 3.4 (Too high 38 S 1 )9 l5 to peel) H X 4.] (Too high 57 (17 )8 Is to peel) 1 X 2.7 24 loo Inn (t J X none Standard No It) (17 I5 5 lb or. N.R. clusters K X (Plus lab. applied 2.6 lUll Hill I()() l mm I. X (Partially removed 2. Light Weight (Too high l5 I4 69 42 by cleaningt It) on to peel) M x 2.3 1.16 62 so Inn 7 2.3 0.7-1 W 0 Inn 5 (Plus lab. applied Table I .-continued Pre-Dip Spray Coating Containment of Bottles \eisus (outing Variables Fragment Containment From Pressurized Production Production 4-Foot Drop Tests Applied Applied Distribution of Bottle As Fragments About The Point of Drop Impact. Percent Es. None TP'l' TP'I' TPT Lab Dip 1 Bottle Peel Percent About Frag- Total 0111 Plus Plus Applied Applied Type Strength of The ments No. of

S(-l Lab Ap- S('-l0ll Blend lbJin." Bottle Point of Inside Fracplied Only No. 7 Con- Frag- A ture SC-l00 Coating" tained in mcnts Radius- Frag- Ap- Largest Residing of moms proxi- Single on 2 Ft. mate. Cluster Foot- From mils I Square Center Impact of Block Impact SC-IUO) "Bottles ere spray ed \\hile hot 3U0IZ in production. ZSIPF. in the lab. I with dilute \\'ater-hased emulsion ol'TP'l (tetr'aisopropyl titunate) and/or SC-Itlll (Polyethylene l.

"H \car 267*) plus 2 parts, H parts 207! of l percent Polyhall 295. ("outings were air-dried and cured 4 minutes in 450F. hot-air oven. Adherence measured for u 2 inch \\iile strip of coating pulled ol'l'at right angles to the bottle surface in a slow continuous motion while measuring the pull in pounds.

In view of the above. it'will be seen that the several objects of the invention are achieved and other advantageous results attained. V i i As various changes could be made in the above products and methods without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A container having improved mechanical service strength and shatter resistance comprising a glass con taincr body. a plastic containment coating film overlying the outside surface of said body and an adherency modifying primer coating between the outside surface of said body and the inside surface of said plastic containment coating film through which the containment film is substantially uniformly adhered to said body but with a peel strength of less than about 1.6 lb/in.. the mechanical properties of said plastic containment coating film being such that. when the film is subjected to tensile testing at room temperature and a film exten sion rate of 10 in./min. said film exhibits a tensile strength of at least about 300 lb/in an elongation of at least about 8071 and a modulus of elasticity in tension which is less than about 1,000 lb/in substantially throughout the course of extension of the film.

2. A container as set forth in claim 1 wherein the peel strength is not substantially greater than about 1.0 lb./in.

3. A container as set forth in claim 1 wherein said adherency modifying primer coating is selected from the group consisting of polyethylene. a silicone resin and montan wax.

4. A container as set forth in claim 3 wherein said peel strength is not substantially greater than about 1 .0 lb./in.

S. A container as set forth in claim 4 wherein said peel strength is between about 0.60 and about 0.70 lb./in.

6. A container as set forth in claim 1 wherein said plastic is an acrylic plastic.

7. A container as set forth in claim 6 wherein said plastic is constituted by a copoly'mcr of ethyl acrylate and acrylonitrile.

8. A container as set forth in claim 1 wherein said copolymer contains approximately 85% by weight repeating units derived from ethyl acrylatc and approximately 12% by weight repeating units derived from acrylonitrile.

9. A container asset forth in claim 6 wherein said film is obtained by curing a coating composition comprising an acrylic latex.

l0. A container as set forth in claim 1 wherein said plastic containment coating film has a thickness of between about 2 and about 5 mils.

11. In a method of imparting improved mechanical service strength to a container having a glass body which comprises applying a plastic containment coating film to the outside surface of said body. the improvement which comprises applying an adhercncy modifying primer coating over the outside surface of said body prior to the application of the plastic c0ntain ment coating film. said primer coating being effective to afford substantially uniform adherence of said plastic coating to said body, but with a peel strength of less than about 1.6 lb/in.; and applying over said primer coating a plastic coating film whose mechanical propcrties are such that. when subjected to tensile testing at room temperature and a film extension rate of 10 in./- min., said film exhibits a tensile strength of at least about 300 lb/in an elongation of at least about and a modulus of elasticity in tension which is less than about 1,000 lb/in substantially throughout the course of extension of the film.

12. In a method as set forth in claim 1, said peel strength being less than about 1.0 lb./in.

13. In a method as set forth in claim 12, said peel strength being between aabout 0.60 and about 0.70 lb./in.

14. In a method as set forth in claim 11, said plastic being an acrylic plastic.

15. In a method as set forth in claim 14, said plastic being constituted by aa copolymer of ethyl acrylate and acrylonitrile.

16. In a method as set forth in claim 15, said copolymer containing approximately by weight repeating units derived from ethyl acrylate and approximately 12% repeating units derived from acrylonitrile.

17. In a method as set forth in claim 14, said plastic containment coating being provided by curing a com position comprising an acrylic latex.

19. in a method as set forth in claim ll, said plastic containment coating film having a coating thickness of between about 2 and about 5 mils. 

1. A CONTAINER HAVING IMPROVED MECHANICAL SERVICE STRENGTH AND SHATTER RESISTANCE COMPRISING A GLASS CONTAINER BODY, A PLASTIC CONTAINMENT COATING FILM OVERLYING THE OUTSIDE SURFACE OF SAID BODY AND AN ADHERENCY MODIFYING PRIMER COATING BETWEEN THE OUTSIDE SURFACE OF SAID BODY AND THE INSIDE SURFACE OF SAID PLASTIC CONTAINMENT COATING FILM THROUGH WHICH THE CONTAINMENT FILM IS SUBSTANTIALLY UNIFORMLY ADHERED TO SAID BODY BUT WITH A PEEL STRENGTH OF LESS THAN ABOUT 1.6 1B/IN., THE MECHANICAL PROPERTIES OF SAID PLASTIC CONTAINMENT COATING FILM BEING SUCH THAT, WHEN THE FILM IS SUBJECTED TO TENSILE TESTING AT ROOM TEMPERATURE AND A FILM EXTENSION RATE OF 10 IN./MIN., SAID FILM EXHIBITS A TENSILE STRENGTH OF AT LEAST ABOUT 300 LB/IN2, AN ELONGATION OF AT LEAST ABOUT 80% AND A MODULUS OF ELASTICITY IN TENSION WHICH IS LESS THAN ABOUT 1,000 IB/IN2 SUBSTANTIALLY THROUGHOUT THE COURSE OF EXTENSION OF THE FILM
 2. A container as set forth in claim 1 wherein the peel strength is not substantially greater than about 1.0 lb./in.
 3. A container as set forth in claim 1 wherein said adherency modifying primer coating is selected from the group consisting of polyethylene, a silicone resin and montan wax.
 4. A container as set forth in claim 3 wherein said peel strength is not substantially greater than about 1.0 lb./in.
 5. A container as set forth in claim 4 wherein said peel strength is between about 0.60 and about 0.70 lb./in.
 6. A container as set forth in claim 1 wherein said plastic is an acrylic plastic.
 7. A container as set forth in claim 6 wherein said plastic is constituted by a copolymer of ethyl acrylate and acrylonitrile.
 8. A container as set forth in claim 1 wherein said copolymer contains approximately 85% by weight repeating units derived from ethyl acrylate and approximately 12% by weight repeating units derived from acrylonitrile.
 9. A container as set forth in claim 6 wherein said film is obtained by curing a coating composition comprising an acrylic latex.
 10. A container as set forth in claim 1 wherein said plastic containment coating film has a thickness of between about 2 and about 5 mils.
 11. IN A METHOD OF IMPARTING IMPROVED MECHANICAL SERVICE STRENGTH TO A CONTAINER HAVING A GLASS BODY WHICH COMPRISES APPLYING A PLASTIC CONTAINMENT COATING FILM TO THE OUTSIDE SURFACE OF SAID BODY, THE IMPROVEMENT SHECH COMPRISES APPLYING AN ADHERENCY MODIFYING PRIMER COATING OVER THE OURSIDE SURFACE OF SAID BODY PRIOR TO THE APPLICATION OF THE PLASTIC CONTAINMENT COATING FILM, SAID PRIMER COATING BEING EFFECTIVE TO AFFORD SUBSTANTIALLY UNIFORM ADHERENCE OF SAID PLASTIC COATING TO SAID BODY, BUT WITH A PEEL STRENGTH OF LESS THAN ABOUT
 1. LB/IN., AND APPLYING OVER SAID PRIMER COATING A PLASTIC COATING FILM WHOSE MECHANICAL PROPERTIES ARE SUCH THAT, WHEN SUBJECTED TO TENSILE TESTING A ROOM TEMPERATURE AND A FILM EXTENSION RATE OF 10 IN./MIN., SAID FILM EXHIBITS A TENSILE STRENGTH OF AT LEAST ABOUT 300 LB/IN2, AN ELONGATION OF AT LEAST ABOUT 80% AND A MODULUS OF ELASTICITY IN TENSION WHICH IS LESS THAN ABOUT 1,000 LB/IN2 SUBSTANTIALLY THROUGHOUT THE COURSE OF EXTENSION OF THE FILM.
 12. In a method as set forth in claim 1, said peel strength being less than about 1.0 lb./in.
 13. In a method as set forth in claim 12, said peel strength being between aabout 0.60 and about 0.70 lb./in.
 14. In a method as set forth in claim 11, said plastic being an acrylic plastic.
 15. In a method as set forth in claim 14, said plastic being constituted by aa copolymer of ethyl acrylate and acrylonitrile.
 16. In a method as set forth in claim 15, said copolymer containing approximately 85% by weight repeating units derived from ethyl acrylate and approximately 12% repeating units derived from acrylonitrile.
 17. In a method as set forth in claim 14, said plastic containment coating being provided by curing a composition comprising an acrylic latex.
 18. In a method as set forth in claim 11, said adherency modifying primer coating being selected from the group consisting of polyethylene, a silicone resin, and montan wax.
 19. In a method as set forth in claim 11, said plastic containment coating film having a coating thickness of between about 2 and about 5 mils. 